Say I want to find all tweets that link to a particular blog post, such as this one, and considering that most tweets would actually use URL shorteners, is there a way to find those tweets, taking into account the tweet might contain the original URL or any of the shortened URLs?

BackTweet's free service has a tweet history for URL searches of between 2 – 4 weeks, and the pro service ($100/month, ouch!) advertises 2 years tweet history. If there's a strong business case, perhaps that's worth it.